As the Bible says, so shall the first be last and the last first (or
something), and so it is with the Sharp-sourced Tandy Pocket Computers as
the PC-1 introduced the line and the PC-8 concluded it, despite the
Casio interlopers PC-4/5/6/7 jumping in the middle.

With the exception of the PC-2, all of the Sharp-built
Tandy Pocket Computers use S'-BASIC, a single-byte tokenizing system with
a limited set of commands.
S'-BASIC (as opposed to S-BASIC, the larger variant which was used in other
Sharp Pocket Computers but only used by
Tandy in the PC-2), which
Tandy dubbed "Pocket BASIC," introduces several
key conceits of Pocket Computer programming that even influenced Casio.
The first and most obvious change is that BASIC is a two-headed chimaera,
split into a pure RUNtime mode where calculations can be
entered in freely (as if it were a calculator) and programs can be executed,
but not edited; and a PROgram (or WRiTe) mode with a simple editor where
programs are entered, changed and overwritten, but no immediate mode statements
can be processed. This allowed easy switching of behaviour without increasing
cost or complexity. Secondly,
S'-BASIC also established the convention of a fixed
baseline variable space, where variables A-Z (or A$-Z$) were defined as a
baseline, double variables weren't allowed (no simultaneous use of A and A$)
and arrays were actually aliases to other variables
within the space (such that A(1) was the same as B). Both of these modes
carried over into their descendants and into the Casio models;
although the S'-BASIC was upgraded with various
small changes, the base interpreter remained essentially unchanged, allowing
the line to be broadly cross-compatible (or at least upwardly so). All
Sharp systems had single programming spaces; to mitigate this limitation,
programs could be subdivided with one touch access to labels using the
"DEF" key -- for example, DEF followed by A jumped to label "A" in
the BASIC text. Although useful for creating menus, this approach was
definitely less elegant than the segmented program spaces of the later Casio
units.

Interestingly, none of the Sharp-based Tandy Pocket Computers (except the
PC-2) has a lower-case mode.

Despite being the elders of the line, there is still much to recommend the
Sharp units, and with the exception of the PC-8, the Sharps (including the
incompatible but obscenely powerful PC-2) demonstrate
generally good design and decent performance in a small package -- exactly what
we would expect from a Pocket Computer.

Tandy Radio Shack TRS-80 Pocket Computer PC-1

The first Tandy Pocket Computer was certainly a bombshell to the American
market -- here was something more powerful than the usual clearance-box
desktop calculator, something you could program and do stuff with in the
palm of your hand!
Just get used to squeezing it all into that little keyboard, and you're
set!

Tandy seemed to know that they were releasing something a little hard for
the casual computerist to grasp. We don't blink an eye today at an iPhone or a
Palm Pilot, but in 1980 Sharp had to work hard to shake the calculator
stereotype ("A truly pocket-sized Computer (not a programmable calculator),"
asserts the manual; "since this is such a radically new product and most
people won't know how or where to start ..."). To that end, giving it its
own dialect of BASIC, even a relatively small one, was a key advancement
setting it on apparent par with larger contemporary
desktop systems since they, too, were often programmed in BASIC.

As stated above, the PC-1 was the standard-setter for the dual-mode BASIC
we see on every Pocket Computer, along with its inventive method of
variable management to make the most of the small space available, and if
one wanted a larger array you could make a bigger one referenced as Z()
by taking program space away.
Although the arithmetic was very good for its class,
string management was best described as inadequate, mostly due to a very
sparse implementation lacking several key operators
and their eight-character length which was set in stone, something Sharp
would try to remedy in future models. The PC-1
also established the peculiar "dot abbreviation" convention of Sharp BASIC:
where an abbreviated instruction was followed by a literal period (.); any
instruction could be abbreviated to its unique portion, which was a little
dubious for things like SI. and CO. but was fairly useful
for longer keywords like PRINT (P.) and
RETURN (R.). Entry was made even more convenient with the
Reserve Keys function, essentially a macro-keys facility where any of a
set of keys (the bottom two alpha rows, minus ENTER) could be programmed with
text up to a combined total of 48 bytes. Debugging was essentially token, but
the DEBUG command did allow rudimentary tracing.

The PC-1 is interesting for its dual-CPU architecture, but this should not
be considered a parallel CPU architecture. The CPUs are basically
the same core with different (mask?) ROM for different features and handle
different services, switching execution back and forth; Roman von
Wartburg believes this occurred because one single CPU was simply
not enough to hold the entirety of BASIC and the BIOS, which seems plausible.
Indeed, the dual CPU approach was never repeated outside of the PC-121x line.

Tape being the dominant (and cheapest) method of mass storage open to most
hobbyists, Tandy simultaneously released the PC-1 with a rebadged Sharp
cassette interface for $49,
powered by AA batteries. Cassette support was very complete -- even reserve
keys could be saved to tape! The cassette-printer interface, the first one to
establish the regrettable convention of NiCad usage (greatly limiting its
longevity in the present era), came later and is not
documented in the baseline manual. This 16CPL 5x7-pin dot-matrix printer used
its own unique ribbon cartridges and retailed for a reasonable $149.95,
although the initial impression of good value
would probably evapourate once you'd waxed the battery. If you find one of
these printers, make sure you get plenty of ribbon since it's not always
easy to come by. It is somewhat inexplicable why a 24-character display
would be chained to a 16-character printer, however.

Tandy wanted to establish its line off right and released a bucket of
home-grown software packages on tape along with the launch covering a wide
variety of applications from games to statistics and business and personal
finance. These packages are difficult to find nowadays, particularly in
intact condition with manuals, but the move was an extremely sound one at
the time and it is surprising that Tandy did not do this more with later
Pocket Computer releases. Most were under $20. There were even a few books
released by Tandy specifically for the PC-1, both of them republished and
store-branded titles.

There is a fault with the PC-1 that was not apparent during its days of
existence but is of great concern to collectors -- over time, many PC-1
LCDs will gradually darken around the traces, and some will turn almost
completely black. This seems to be caused by inadequate sealing around the
LCD assembly causing the crystals to gradually dehydrate and become opaque
with time. If you are looking for a PC-1 to purchase, inspect the display
carefully and pick a unit that looks as clear as possible. Fortunately,
it does not seem to affect all units as there are many that are still
pristine.

Although an exceptional first start, the PC-1 is still largely outclassed by
the majority of its successors in just about every metric including
size, memory and performance. Nevertheless, this should not
be considered an intrinsic failing, merely the natural progression of a
design where this unit was clearly the prototype, and at the time a
practically revolutionary one. Indeed, the extremely easy
availability of the PC-1 on the used market should bear ample testimony to
the number that were sold. Tandy discontinued the model in 1983.

Here are the Tandy options/catalogue numbers and their Sharp equivalents
for the PC-1:

26-3503 cassette interface (Sharp CE-121)

26-3505 cassette and printer interface (Sharp CE-122)

26-3506 printer paper 1-25/32" wide, 31/32" diametre

26-3507 printer ribbon

26-3508 vinyl carrying case (a very nice faux leather case with pockets
and satiny interior, but is only labeled 'TALON' and not TRS)

Tandy Radio Shack TRS-80 Pocket Computer PC-3

With the PC-3, Tandy cloned their smallest Pocket Computer yet and as
such the one most deserving of the name;
the PC-1 needed deep shorts
to accomodate it, and the PC-2 was positively
acromegalic. Even the just slightly
preceding PC-4 looked buff by comparison.

Best of all, despite its considerably smaller size, it is still a Pocket
Computer with Punch; how much Punch is currently a matter of some research
and debate, however.
Most resources agree that its clock speed is 576kHz, a nice bump over the
PC-1, except that the (admittedly embryonic) PC-1251 MESS
driver insists on a more pedestrian 192. Tandy also in their official
specifications for the units insisted that an additional 0.2K of RAM was
present in the total, an assertion that appears in no other references; it
isn't at all clear
where this is coming from, although it may possibly represent a
contribution from whatever RAM is buried in the display controller.
(The memory specs I have presented are purely based on RAM chip presence.)

Whatever the real numbers, it did the job and it fit in your pocket. The PC-3
took all the PC-1's best features, including the screen, reservable
keys and definable keys, and put them into a faster, smaller and sleeker
package. Free memory was about the same, but didn't get any worse for size,
and in 1983 the MSRP of $99.95 was a steal.
In addition, the PC-3 had an upwardly compatible BASIC, strongly based
on many facets of the PC-2's -- while
tapes saved on a PC-1 could be read into a PC-3 as-is, PC-3 programs could
take advantage of added support for READ/DATA/RESTORE, WAIT, RANDOM,
INKEY$ and
PASSword protection, while DEBUG was changed out for the more typical
TRON/TROFF. Strings and array support were greatly improved with a new
two-dimensional DIM, and arrays other than A() were independent and did
not alias other variables (but the only array that could be used as a
second subscript was, strangely, A()); in addition, DIM not only
controlled array size but allowed string expansion with constructions like
DIM B$(3)*12, which creates four (0-3) 12-character strings. Strings
defaulted to 16 characters, but could be as long as 80.
The glitch with 2-D array
subscripting must have escaped the notice of the manual authors
because it was hastily published on an easily-misplaced slip of paper after
the manual's initial publication.

The presence of the PC-3 really helped bring old PC-1 users back into the
fold, especially with the incompatibilities of the PC-2
and PC-4.
Really, there were only two small stains on the PC-3: the fact that available
free memory really didn't improve much, and the loss of the PC-1's peripheral
port. I call these "small stains" because the latter was largely mitigated
by the large variety of Sharp peripherals that the PC-3 was compatible
with, and the memory constraint was tremendously lightened with the 4K PC-3
"PC-3A"
released in 1984. (One "thing that makes you go hmm" is the lower catalog
number for the later release ... perhaps releasing the 4K PC-3 was
something Tandy was planning from the beginning?) Tandy also simultaneously
released their own thermal printer and tape interface for an MSRP of $119.95,
finally with a 24CPL width, bringing the PC-3's
peripheral availability to par with its older relative.

The 4K PC-3 was the first Pocket Computer to lose the Radio Shack designation,
becoming merely the Tandy Pocket Computer PC-3, or PC-3A as it appeared
in some catalogues. Replacing its predecessor completely, the 4K PC-3 "PC-3A"
lasted until 1986.

The PC-3, along with the PC-2 and
PC-4, easily represents the best of what Pocket
Computers have to offer. In fact, although the
PC-4 beats the PC-3 in cost and convenience and
the PC-2 just crushes everything under its
raw oozing muscle, the 4K PC-3
makes a decently fast, amply provisioned, good all-around system --
especially when paired up with all the
compatible peripherals Sharp made and Tandy didn't import! Many people
will talk in reverent tones about the Sharp
CE-125, a very cleverly designed printer
and microcassette recorder combination which looks super-neat in its matching
case, but unfortunately was another evil NiCad-based
contraption that I have recently learned works well to prop my closet open
('cuz when the battery goes toes up
it sure don't do squat else). Instead, I rave about the Sharp CE-126P,
another cassette/printer combo which can be powered with AA batteries, using
the same thermal printer paper as the PC-3's own native printer.
This stylish portable device
is not hard to find on the used market -- I own two, both purchased from eBay
originally -- and because it is a relatively unknown device does not command
a large price. A PC-3 and a CE-126 are a hard-to-beat combination for a small
desktop print terminal or for running printed tallies off of calculations,
and the built-in cassette interface is a nice bonus. Need something to run
off raffle tickets? Need to spin out numbers on paper without waiting for
Excel or Mathematica to start up? Want a receipt printer that's a little
more than an adding machine? You can't beat this combo for size or convenience.

Another outstanding find, but a tough one, is the small 2.5" CE-140F
pocket floppy drive. Although the media is weird, you get a comfy 64K
per side, enough to jam just about anything you want on a single disk.
Finally, the (much later) EA-128C and EA-129C can be used as a link
cable between the PC-3 and any Sharp system with the same 11-pin I/O.

The long and short of it is,
for a great combination of size, expandability and function, the PC-3
definitely deserves consideration by anyone who wants a Pocket Computer that
can "do real stuff."

The cross-platform MESS multiple systems
emulator has a driver for the PC-1251, which will work for PC-3 emulation,
of course.

The pinout for the 11-pin I/O connector is as follows (pin 1 starting from
the top of the machine). They should be 5v TTL levels, but I am not
responsible if you fry your machine, so test carefully.

MT 2 (optional input from peripheral)

Ground

VCC

Busy

Data Out (typically for printer)

Cassette Out (a/k/a X out)

Cassette In (a/k/a X in, MT 1)

Data In

ACKnowledge line

IO select 2 (optional select line driven by computer)

IO select 1 (optional select line driven by computer)

Here are the Tandy options/catalogue numbers for
the PC-3 series. Note that the software sold for the PC-1 was also included
in ads for the PC-3, despite being exactly the same and having the same
catalogue numbers, so I will not repeat them here.

26-3591 cassette/printer interface. I can't find a Sharp equivalent for
this, and may have been a custom one-off, but it appears to be
Sharp-manufactured.

26-3592 thermal paper

Other sites on the PC-3 (note that not all acknowledge the 4K version):

Tandy Pocket Computer PC-8

When Tandy is determined to foul up, they just keep right on doing it.
While Sharp saw fit to make a low-cost version of the PC-125x series in 1983,
which started as the 8-bit PC-1245 and was then mutated down into the even more
watered-down 4-bit
PC-1246, Tandy didn't see fit to import it until 1987, essentially
the same mistake they made with the dreadful PC-7.

The shame is that the PC-1246 is judged unfairly by many unfamiliar with Sharp
because of the tardiness of the PC-8, when in reality it was not at all
dismal compared with its contemporaries at the time of its initial
development. As a low-cost version of the PC-1250/PC-1251,
it did achieve its market purpose, and it is the lightest yet
easily the most durable of the Pocket Computers with its rugged hard case --
durability being
a quality many Pocket Computers, even the ones Tandy didn't import, seriously
lacked, and it is in fact the only Tandy Pocket Computer that does
have such a rigid case.
It also sported the same 11-pin I/O port, meaning it could accept
PC-125x peripherals, and its BASIC was completely compatible such that anything
that could tolerate the smaller screen would run without modification
otherwise. Although it lacked reservable keys, something sorely missed, it
did offer keyword key combinations and
could still simulate reserve keys
in a limited sense with the defined key function and some programming.
Finally, the free memory count when compared with the PC-1250 was
nearly equal.

For 1983, then, the PC-1246 was adequate, but in 1987 it was pointless.
Although the MSRP was not unreasonable, at $59.95, it merely appeared as
decent as it did solely when compared to the underpowered, unexpandable and
low quality PC-7. While a step up from that
preceding unmitigated
disaster (and $10 less to boot),
it was still a dismal way to finish the Tandy Pocket Computer series but
incredibly was in fact outsold and outlasted by those very same ancestors.
Along with the PC-5, it had one of the shortest
lifetimes of any Pocket Computer, lasting less than a year.

The PC-8 is fully compatible with all PC-3 peripherals, so no special
peripherals unique to it
were produced, and the PC-2's large travel case was
also billed as compatible.